Fuel Pump whine. Louder with lights off? Odd?

[IS300E30]

My fuel pump under driver side is whining. The odd part, is that it sounds a lot louder when my lights are off, when my lights are on it still whines but not nearly as loud?

Isn't it odd that the loudness of the whine sound changes depending if my lights are on or off?

[gonomo]

Your fuel pump is probably going bad. As for the whine changing, it could mean that your battery is not functioning 100% and could be putting wear on your alternator. I’m not an expert though, that’s just my 2 cents.


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[e30davie]

When you turn the lights on you are drawing more current, and the voltage at the pump is probably a bit lower. what you are hearing is the pump running on say 13.5 volts with lights off, but when you turn the lights on the voltage drops to say 13.2.

And when pumps run on different voltages the apparent noise can change.

I would have a look at your alternator and make sure its charging properly (~13.5v at the battery). If the alternator is charging properly what you describe is probably not a big deal.

The other thing you can do is actually measure the voltage at the noisy pump. Might pay to check the connections on the pump too, might be a bit of shit on the connections which is increasing the resistance (voltage drop and thus more noise)